Over the past two decades, child welfare agencies have seen increases in the number of foster children in their care. The fact that foster children today have complex health care (especially mental health care) needs has become increasingly well understood. In an attempt to find financial resources to serve these needs, child welfare agencies have developed significant dependence upon Medicaid. But Medicaid itself has undergone significant changes in its organization and financing, and the impact of such changes on access to health care services for children in foster care is largely unknown. This study examines the impact of Medicaid managed care and Medicaid eligibility policy on access to mental health services for children in foster care. Specifically, it examines the effects of three Medicaid managed care policies-enrollment into Medicaid managed care; behavioral health carve-outs under Medicaid managed care; and varying models of Medicaid managed care service delivery-and the effects of state policies that make foster children categorically eligible for Medicaid on three measures of access to mental health services-mental health provider visits; number of such visits; and use of psychopharmacological medication-for children in foster care. This study analyzes data from the National Survey of Child and Adolescent Well-Being (NSCAW), the first nationally representative survey of children and families in child welfare. County-level Medicaid policy variables are obtained from a study designed to parallel NSCAW. Using clustering corrections to account for non-independence of foster children within counties, the study develops logit, probit and Poisson models to estimate the effects of the above listed Medicaid policies on access to mental health care. This study will thus use national-level data to examine the interface between child welfare and health care systems. Findings from this study will inform state health policymakers as well as child welfare policymakers in their attempts to provide funding for the services that are required by foster children nationwide.